1. Technical Field
The present disclosure herein relates to electronic devices and methods of fabricating the same and, more particularly, to energy harvesting devices and methods of fabricating the same.
2. Description of Related Art
Recently, diverse electronic devices have been produced with development of electronic communication technologies. For example, the electronic devices such as portable electronic devices have been abruptly in demand since the portable electronic devices can be realized with user-centered ubiquitous products. The portable electronic devices may need portable power supplies such as batteries. However, there may be some limitations in using the batteries because the batteries may be disposable or should be periodically recharged. Accordingly, the necessity of energy harvesting technologies and energy harvesting devices may be increasingly required to effectively use the portable electronic devices.
The energy harvesting technologies mean techniques that convert mechanical energy wasted in nature into electric energy. The mechanical energy wasted in nature may includes vibration energies generated by vibrations of trains, vibrations of vacuum pumps, vibrations of mechanical motors, vibrations of automobile engines and human movements. Since the energy harvesting devices become extremely miniaturized according to application areas thereof, many efforts have been concentrated on micro-electro-mechanical system (MEMS) vibration energy harvesting devices utilizing piezoelectric characteristics, which are appropriate for power supplies of micro devices. Typical vibration energy harvesting devices using the piezoelectric characteristic may have a cantilever structure.
The cantilever structural energy harvesting devices fabricated using MEMS techniques may have infinite possibilities as self power supplies of remote control systems corresponding to wireless sensor nodes. The cantilever structural energy harvesting devices using the vibration energies may generate a high output power in response to a low resonance frequency which is equal to about 100 Hertz or less. Resonance frequencies generated in a general environment may be within a low frequency band. Accordingly, the energy harvesting devices may produce a high energy in the general environment where human beings live.
However, the conventional energy harvesting devices are fabricated in a single mode on a silicon wafer based on the MEMS technique. Thus, the conventional energy harvesting devices may exhibit a low energy harvesting efficiency. Further, according to the conventional energy harvesting devices, it may be difficult to control the resonance frequency of a cantilever.